An engine control module of an internal combustion engine controls the mixture of fuel and air supplied to combustion chambers within cylinders of the engine. After the air/fuel mixture is ignited, combustion takes place and later the combustion gases exit the combustion chambers through exhaust valves. The combustion gases are directed by an exhaust manifold to a catalytic converter or other components of an exhaust aftertreatment system. Some engines optionally may include a forced air induction device, such as a turbocharger, that is positioned between the exhaust manifold and exhaust aftertreatment components.
Manufacturers of internal combustion engines, particularly diesel engines, are presented with the challenging task of complying with current and future emission standards for the release of nitrogen oxides, particularly nitrogen monoxide, as well as unburned and partially oxidized hydrocarbons, carbon monoxide and particulate matter. In order to reduce emissions of internal combustion engines, an exhaust gas aftertreatment system is used to reduce regulated constituents from the exhaust gas.
Exhaust gas aftertreatment systems typically include one or more aftertreatment devices, such as particulate filters, catalytic converters, mixing elements and urea/fuel injectors. Control of temperature of the exhaust gas can affect the performance of components within the exhaust system. For example, catalytic reduction devices may have to be warmed up to an operating temperature range to perform the desired catalytic reaction and thus effectively treat selected exhaust gas constituents.
In addition, a speed of a diesel engine (revolutions per minute or RPM) may be controlled by the amount of fuel injected into the cylinders for combustion. Thus, reductions in engine speed are typically achieved by reducing or shutting off fuel injection to the cylinders. After reducing fuel supply to the cylinders, air continues to flow through the cylinders and into the exhaust system, wherein the air can cause cooling of exhaust system components to temperatures below their operating temperatures.